1. Field of the Invention
The present invention relates to a hydrocracking catalyst and a hydrocracking method for hydrocarbon oils, and more specifically, it relates to a hydrocracking catalyst with excellent hydrocracking performance for heavy petroleum distillates such as vacuum gas oil, and to a hydrocracking method using the catalyst which gives middle distillates as the major products.
2. Background Art
Recent years have seen an increased demand for light petroleum products, while heavy types of crude oil have tended to become more available. This has further increased the important role of heavy oil cracking apparatuses.
Various different hydrocracking catalyst compositions and preparation processes for heavy oils have been proposed. The major catalysts are known as dual function catalysts, i.e. catalysts that exhibit both hydrogenation activity with carried metals and cracking activity with solid acids of carriers. Among these the most common are catalysts employing carried metals that are combinations of nickel or cobalt, metals of Group 8 of the Periodic Table, and molybdenum or tungsten, metals of Group 6a of the Periodic Table. Most well known are double oxides such as silica-alumina, which are large surface area carriers with solid acidity.
A few systems are also known which employ ternary complex oxides as carriers. For example, Japanese Unexamined Patent Publication No. 58-210847 discloses a system wherein silica or magnesia are added as secondary components to alumina-titania, and Japanese Unexamined Patent Publication No. 58-210993 discloses a system wherein a ternary complex oxide comprising alumina, titania and zirconia is used as the carrier. These publications disclose improvements in demetalization activity on heavy oils.
In Japanese Unexamined Patent Publication No. 58-219293 it is disclosed that effective hydrocracking of heavy oils can be accomplished with catalysts having hydrogenating metals carried on carriers containing alumina as the main component and at least one inorganic oxide selected from among silica, titania, zirconia, boria and phosphia, or carriers containing titania as the main component and at least one inorganic oxide selected from among alumina, silica, zirconia, boria and phosphia.
However, in systems employing the above-mentioned amorphous complex oxides as carriers, there is a limit to the improvement in catalytic activity, while the effect of increased middle distillates is inadequate.
Numerous catalysts are known containing zeolites in addition to the above-mentioned complex oxides. Zeolites suitable as hydrocracking catalysts include synthetic Y-type zeolite, and Y-type zeolite stabilized by various treatments. Zeolite has a higher acid density compared to amorphous complex oxides. Zeolite used by itself has high cracking activity but causes overcracking, resulting in a lower middle distillate yield. The purpose of the stabilization treatment mentioned above is to lower the unit lattice constant of the zeolite, reduce the acid density and improve selectivity. For example, Japanese Patent No. 2562322, No. 2563910 and No.2619700 disclose hydrocracking methods aimed at selectively improving the middle distillate yield by a catalyst containing Y-type zeolite with a low unit lattice constant.
However, using catalysts with the compositions and physical properties described in these Japanese patents cannot give adequate cracking activity and middle distillate selectivity. This means that until now, due attention has not been given to the properties which reflect zeolite function.